The present invention relates to a method for soldering electric and or electronic components to printed-circuit boards using a pool of molten solder.
It has been well known heretofore that electric and or electronic components including chip type components temporarily fixed to a printed-circuit board are soldered to the circuit board by dipping the circuit surface into a static pool of molten solder. In such a soldering system, generation of flux gas and gas from the printed-circuit board itself takes place in a soldering operation and the gases tend to accumulate around terminal portions of the components to be soldered. The accumulated gases interfere with uniform soldering of the components to the circuit board. In order to eliminate this disadvantage, it has been a practice to position vent holes formed in the circuit board adjacent terminals of the components to be soldered. However, the existence of the vent holes results in a restriction of the circuits to be formed on the other surface of the board, preventing the circuits from being highly concentrated. Moreover, formation of the vent holes in the circuit board results in a high cost and a reduction in the strength of the board.
An attempt has been made to expel generated gases out of the terminal portions of the components by means of a high speed jet flow of molten solder towards the components. Such a soldering system is successfully applied to relatively thin flat chip components, but still there is a need for formation of vent holes to effect complete expelling of the gases in case that the soldering system is applied to large cylindrical chip components normally called metal electrode facebonding type components and mould type-transistors. Moreover, in this soldering system, uniform soldering can not be achieved because of the generation of waves on the top surface of the molten solder.
Accordingly, a main object of the present invention is to provide a novel and useful method for soldering to a printed-circuit board, electric and or electronic components temporarily fixed thereto while preventing flux gases which are generated in the soldering operation from accumulating around terminal portions of the components.
Another object of the present invention is to provide a method of the above-mentioned kind comprising conveying printed circuit board having the components temporarily fixed thereto along the top of a pool of molten solder, generating bubbles by blowing gas into the molten solder, the bubbles rapidly rising in the molten solder toward its top, and striking the rising bubbles against the circuit surface to expel any flux gases which otherwise would accumulate around terminal portions of the components and to solder the components to the board.